1. Field of the Invention
The present invention relates to a surface acoustic wave device and a method of manufacturing the same. More specifically, the present invention relates to a surface acoustic wave device having an improved structure and a method for manufacturing the same.
2. Description of the Prior Art
Since a surface acoustic wave device has superior electrical characteristics, such as frequency characteristic and the like, as compared with many other devices, recently, attempts have been made to put the same into practical use in various fields. Such a surface acoustic wave device requires a package such as a hermetic seal structure, a resin mold structure and the like which are well-known. However, a difficulty of fabrication thereof peculiar to a surface acoustic wave device has been a hindrance to an improvement in mass productivity of a surface acoustic wave device having a package structure, which has been one cause that makes it difficult to reduce the cost of such a device.
For example, in case of a hermetic seal structure, wire bonding is employed for connection from an element to leadout terminals connecting to an external circuit. Although automation technology for such wire bonding has been considerably advanced, a satisfactory yield has not been yet attained. In the case of a surface acoustic wave device, the elements to be wire bonded are formed of the same electrode material define a transducer region, i.e., an interdigital electrode. Such electrode material is not necessarily a material which is suited for wire bonding and thereto it is necessary to carefully select a material for wire bonding. Since such wire bonding is effected before an element or substrate is packaged, such wire bonding work can exert an unfavorable influence upon an interdigital transducer. If and when an interdigital transducer is subjected to moisture or is damaged during wire bonding work, adjacent electrode fingers of the interdigital electrode can be short-circuited, with the result that the electrical characteristic of the wave device is degraded and cannot be used in extreme cases.
When a package is formed by means of resin dipping, lead-out terminals must be soldered directly to the lead-out electrodes of an element or substrate before the resin dipping process is initiated. Since the substrate is exposed in such a case, the interdigital transducer may be damaged during the soldering process. Furthermore, in case of resin dipping, if and when dipping resin is adhered to a propagation region of a surface acoustic wave of the interdigital transducer, the resin may excert an unfavorable influence upon the characteristics and in order to avoid such influence it has been a common practice that the substrate is provided with a cap to form a necessary gap and is subjected to resin dipping. However, even in case of resin dipping of a device as capped, again an interdigital transducer is liable to be damaged by such a cap and is also liable to get wet. Furthermore, it is difficult to automate the above described soldering process of lead-out terminals. Nevertheless, if such a process is automated, then again an interdigital transducer is more liable to be damaged.